The invention relates to the use of water-redispersible polymer powder compositions having cationic functionality as flocculation aid.
Flocculation aids are used wherever solid-liquid separation is desired. The flocculation aids are used in solid-liquid separation processes such as the cleaning of communal and industrial wastewaters in water treatment plants, the processing of process and circulation water, and the treatment of untreated and surface water to obtain service water and drinking water. The flocculation aids accelerate the sedimentation or flotation of suspended solid particles and bring about a crucial improvement in the dewatering characteristics of the sludges thus thickened in static or machine dewatering methods. Furthermore, the dewatering of sludges is a process where the important factor is to remove the maximum amount of water from the sludges with minimum expenditure.
To date, almost exclusively polymers based on acrylamide or copolymers of acrylamide and cationic monomers such as diallyldimethylammonium chloride (DADMAC) have been used as flocculation aids. A problem is that acrylamide is classified as carcinogenic and, as a consequence, there are bans on the use thereof in some countries or at least plans to impose them. In addition, in the case of use of polyacrylamide products, because of the residual acrylamide monomer content, the landfill disposal and reuse of dewatered sludge in agricultural areas is banned.
As an alternative to the conventional flocculation aids, therefore, polymers of diallyldimethylammonium chloride (DADMAC) have been used (brochure: Polyelektrolyte entwässern Klärschlämme optimal [Polyelectrolytes Achieve Optimal Dewatering of Sewage Sludges], publisher: Deutsches Zentrum für Luft-und Raumfahrt e. V. [German Aerospace Center], Bonn, January 2003)
(cleaner production.de/fileadmin/assets/pdfs/Externe_Projektbeschreibungen/Polyelektrolyte.pdf)
The efficiency of the use of poly-DADMAC in water treatment was examined in W. John et al., Synthesis and Use of PolyDADMAC for Water purification, May 2002
(http://www.ewisa.co.za/literature/files/127%20Paper.PDF). A disadvantage of poly-DADMAC is the relatively high costs of these polymers.
The problem addressed was therefore that of providing polymers of cationic monomers in an administration form which makes them suitable for use as flocculation aids in minimum amounts,
It has been found that, surprisingly, water-redispersible polymer compositions having cationic functionality are of excellent suitability as flocculation aids. Polymer powder compositions of this kind contain cationic polymers which have been used as protective colloids for stabilization during the polymerization or as drying aid in the course of drying of the corresponding polymer dispersions.
EP 0 770 640 A2 discloses water-redispersible polymer powders which are obtained by drying a polymer dispersion after addition of a positively charged polyelectrolyte. The powders thus obtained are recommended as binders in hydraulically setting materials, paints and adhesives. There is no description of use as flocculation aids.
WO 00/05275 A1 and WO 00/05283 A1 disclose water-redispersible polymer powder compositions having cationic functionality which are obtained by polymerizing ethylenically unsaturated monomers in the presence of cationic monomers, and spray-drying the polymer dispersion thus obtained with polyvinyl alcohol as drying aid. The polymer powders thus obtained are described as being suitable for use in adhesives, coating compositions, hydraulically setting building materials, as filler materials in chromatography columns and as carrier for delayed release of active ingredients. There is no description of use as flocculation aids.
WO 2007/093551 A1 and DE 102013223305 A1 describe water-redispersible polymer powder compositions having cationic functionality, which are obtained by free-radically polymerizing ethylenically unsaturated monomers in aqueous medium, and drying the polymer dispersion obtained after addition of a cationic protective colloid. Described examples of the use of these products are application in chemical products for construction, and use in adhesives and coatings. There is no description of use as flocculation aids.
WO 2005/023885 A1 describes a pulverulent, water-soluble, cationic polymer composition containing at least two cationic polymers of different molecular weight, a first cationic polymer being formed in the presence of a second cationic polymer by the method of gel polymerization, and the gel thus obtained being mechanically comminuted. The powder is used as flocculation aid.